This month, I want to identify and briefly discuss the top seven reasons I see that pasture weed control programs don't work as well as they should. A popular comedian has a top 10 list for his act, but since I'm only about 70 percent as funny as he is, I only have a top seven list.
Number 7. Spraying too early (You hit 'em where they ain't.)
Many times, ranchers spray for weeds at a specific date on the calendar – May 1, for example. This works most of the time. However, what happens if the weather is not exactly average that year? If it's colder than average that spring, the weeds may not have emerged when you spray. You can miss them altogether by spraying too early, i.e., when the weeds are not there yet. The solution to this one is obvious – scout the fields and spray the weeds at the proper time based on stage of growth of the weed.
Number 6. Misidentification of the weed (What was that sucker, anyway?)
All weeds are not created equal in their willingness to die from our herbicide program. Try as you might, you're not going to kill a grass or sedge with 2, 4-D unless you set the container on top of it and leave it. Among broadleaf weeds, some tougher weeds to control are more susceptible to different products. Scout your fields and learn to identify the weeds. If you don't know what one is, ask someone who knows. After you've properly identified the weed, look at herbicide labels and find one that controls it.
Number 5. Bad environmental conditions (It's never too dry to spray...)
On about all weeds I can think of, control declines precipitously when they are in drought stress. The plants are merely trying to survive – they are not actively growing and taking up the herbicide in droughty conditions. While it may never be too dry to spray, it can be too dry to get good results. In addition to soil moisture, pay attention to wind speed and direction to control off-target drift. Life is much simpler when you kill weeds on your property and avoid killing the neighbor's garden.
Number 4. Sprayed at the wrong growth stage (I got to it when I could.)
Most weeds are best controlled when they are young and actively growing. When they get larger, it takes more herbicide to kill them, and control is much more erratic. Horsenettle and blackberries are an exception. Control of both of these is best when they are in full bloom or have fruit on them. Spraying them too early results in a top kill, but regrowth usually occurs. Read the label carefully to determine timings for specific weeds.
Number 3. Used the wrong product (What's the cheapest thing you've got?)
Often, the cheapest herbicide will do as well as anything else. This is true when the weeds fall into the easy-to-control category and conditions are ideal for control. For difficult-to-control weeds (Sericea lespedeza and horsenettle, for example), more expensive chemicals are usually needed. Going the cheap route can be good if you do an excellent job of observing the cautions listed previously in this article, but may not work if conditions are less than ideal.
Number 2. Didn't calibrate sprayer (I think a tankful covers somewhere between 10 and 50 acres.)
I don't think it's an exaggeration to say the majority of ranchers don't calibrate their sprayers. This is a practice that should be done every season. Calculating the volume you spray is critical to knowing how much product to put into the tank. When you calibrate, also inspect nozzles, screens, lines, pump, etc., to make sure everything is OK. If you don't know how to calibrate a sprayer, the Noble Foundation soil and crops discipline has instructions for calibrating both boom and boomless sprayers. This is free to residents of Oklahoma and Texas and is available for a small fee to residents of other states.
Number 1. Didn't read the label (There's a lot of really small type on that thing.)
Reading the label covers all the other points mentioned. The label contains safety considerations, product use, container disposal and any other information about the product you need to know. Failure to follow labeled directions can not only lead to poor weed control, it is also a violation of federal law. Following the directions on the herbicide label is about the closest thing to getting a guarantee on weed control I can come up with.
There are many ways to conduct a weed control program that will work. Unfortunately, there are even more ways that will not work. The best chance for success lies in minimizing the incorrect ways.